1. Field of the Invention
This invention concerns a flux for overlay welding, and more particularly to a flux for electro-slag overlay welding with strip electrode (hereinafter referred to as "ES overlay welding" for brevity) in flat position, which is capable of forming clean surfacing bead and is improved in slag detachability with reduced slag remains (hereinafter "slag remain" means that even fine slag can not be removed from the surface of the bead.)
2. Description of the Prior Art
Fluxes for the ES overlay welding are disclosed, for example, in Japanese Patent Publication No. 53-29657 and Japanese Laid-Open Patent Specification No. 55-165294, and in most cases contain CaF.sub.2 and Al.sub.2 O.sub.3 as major components along with oxides such as silica and iron oxide. However, sometimes the conventional fluxes of this sort have a serious problem in that a great deal of time and labor is required for peeling off and removing remained slag which sticks on the bead surfaces in a considerable degree. This tendency is conspicuous especially in the case of Type 347 which is used widely, for instance, for overlay welding on inner surfaces of petroleum refining reactors. In such a case, it takes considerable labor and time to remove the slag from the surfaces of beads which sometimes measure 2 to 4 meters in inside diameter and 20 to 30 meters in length. If the removal of slag is incomplete, there will arise the problem of slag inclusion in the next pass of the welding operation, resulting in a defective weld. Therefore, there has been a strong demand for a flux for ES overlay welding, which can form easily detachable slag.